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\begin{equation*}{\partial^2 Ψ \over \partial x^2\} + {\partial^2 Ψ \over \partial y^2\} + {\partial^2 Ψ \over \partial z^2\} = {1 \over v^2\} {\partial^2 Ψ \over \partial t^2\}\end{equation*}
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